Dual sensor camera

ABSTRACT

A dual sensor camera that uses two aligned sensors each having a separate lens of different focal length but the same f-number. The wider FOV image from one sensor is combined with the narrower FOV image from the other sensor to form a combined image. Up-sampling of the wide FOV image and down-sampling of the narrow FOV image is performed. The longer focal length lens may have certain aberrations introduced so that Extended Depth of Field (EDoF) processing can be used to give the narrow FOV image approximately the same depth of field as the wide FOV image so that a noticeable difference in depth of field is not see in the combined image.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/727,973 (now U.S. Pat. No. 8,542,287), entitled “DUAL SENSOR CAMERA,”filed on Mar. 19, 2010 by at least one common inventor, which claimspriority under 35 U.S.C. 119 to U.S. Provisional Application No.61/161,621, entitled: “DUAL SENSOR CAMERA,” filed on Mar. 19, 2009, bothof which are incorporated herein by reference in their entireties.

BACKGROUND

Digital camera modules are currently being incorporated into a varietyof host devices. Such host devices include cellular telephones, personaldata assistants (PDAs), computers, and so forth. Consumer demand fordigital camera modules in host devices continues to grow.

Host device manufacturers prefer digital camera modules to be small, sothat they can be incorporated into the host device without increasingthe overall size of the host device. Further, there is an increasingdemand for cameras in host devices to have higher-performancecharacteristics. One such characteristic that many higher-performancecameras (e.g., standalone digital still cameras) have is the ability tovary the focal length of the camera to increase and decrease themagnification of the image, typically accomplished with a zoom lens, nowknown as optical zooming. Optically zooming is typically accomplished bymechanically moving lens elements relative to each other, and thus suchzoom lenses are typically more expensive, larger, and less reliable thanfixed focal length lenses. An alternative approach for approximatingthis zoom effect is achieved with what is known as digital zooming. Withdigital zooming, instead of varying the focal length of the lens, aprocessor in the camera crops the image and interpolates between thepixels of the captured image to create a “magnified but lower-resolutionimage.

There have been some attempts to use two different lenses to approximatethe effect of a zoom lens. It has been done in the past with filmcameras in which the user could select one of two different focallengths to capture an image on film. More recently, a variation on thisconcept with camera modules has been disclosed in U.S. Pat. Pub. No.2008/0030592, the entire contents of which are incorporated herein byreference, which discusses a camera module with a pair of sensors, eachhaving a separate lens through which light is directed to the respectivesensor. In this publication, the two sensors are operated simultaneouslyto capture an image. The respective lenses have different focal lengths,so even though each lens/sensor combination is aligned to look in thesame direction, each will capture an image of the same subject but withtwo different fields of view. The images are then stitched together toform a composite image, with the central portion of the composite imagebeing formed by the relatively higher-resolution image taken by thelens/sensor combination with the longer focal length and the peripheralportion of the composite image being formed by a peripheral portion ofthe relatively lower-resolution image taken by the lens/sensorcombination with the shorter focal length. The user selects a desiredamount of zoom and the composite image is used to interpolate valuestherefrom to provide an image with the desired amount of zoom.Unfortunately, the disclosure in this publication is largely conceptualand lacks in certain details that would be needed to provide optimalperformance.

The foregoing examples of the related art and limitations relatedtherewith are intended to be illustrative and not exclusive. Otherlimitations of the related art will become apparent to those of skill inthe art upon a reading of the specification and a study of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a camera.

FIG. 2 is an illustration of the combination of two images into a singlecombined image.

FIG. 3 is an illustration of digital zooming of the combined image.

DETAILED DESCRIPTION

The following description is not intended to limit the invention to theform disclosed herein. Consequently, variations and modificationscommensurate with the following teachings, and skill and knowledge ofthe relevant art, are within the scope of the present invention. Theembodiments described herein are further intended to explain modes knownof practicing the invention and to enable others skilled in the art toutilize the invention in such, or other embodiments and with variousmodifications required by the particular application(s) or use(s) of thepresent invention.

A camera 10 is shown in FIG. 1. The camera 10 may include a first lens12 having a relatively-shorter focal length and a first sensor 14 thatare located proximate to and substantially aligned with a second lens 16having a relatively-longer focal length and a second sensor 18. Byhaving the combined first lens and first sensor aligned with thecombined second lens and second sensor, the sensors can each obtain animage of substantially the same subject. Of course, due to the differentfocal lengths of the lenses 12 and 16, the first sensor 14 will obtainan image of the subject with a relatively-wider field of view (FOV) ascompared to the relatively-narrower FOV of the image obtained by thesecond sensor 18.

In most cases, each sensor 14 and 18 would perform certain basic imageprocessing algorithms such as white balancing, and so forth. The secondlens 16 has an additional reference number 17 to indicate that it isdesigned to work with Extended Depth of Field (EDoF) processing, whichmay involve introducing specific monochrome or chromatic aberrationsinto the lens design as determined by the EDoF technology, or by addinga phase mask (e.g., a cubic phase mask) to the lens. Each sensor mayalso perform additional image processing such as EDoF processing. Inthis example, the EDoF processing 20 is shown as part of sensor 18 andis not a part of sensor 14. In other examples, not illustrated here,each of the sensors 14 and 18 may include EDoF processing, or othercombinations may be employed such as sensor 14 including EDoF processingwhile sensor 18 does not. Similarly, while this example shows only thesecond lens 16 being designed to work with EDoF processing, any othercombination may be possible, including each of the lenses 12 and 16being designed to work with EDoF processing. The lenses 12 and 16 couldbe made of any acceptable material, including plastic, glass, opticalceramic, diffractive elements, or a composite.

EDoF processing will be discussed here generally, but much greaterdetail can be found in the literature associated with the followingcompanies that are believed to be actively developing EDoF technology:DxO Labs, S.A. of Boulogne, France (under its DIGITAL AUTO FOCUS™trademark); CDM Optics, Inc. of Boulder, Color. (under its WAVEFRONTCODING™ trademark); Tessera, Inc. of San Jose, Calif. (under its OPTIMLFOCUS™ trademark); and Dblur Technologies Ltd. of Herzliya Pituach,Israel (whose relevant IP assets are now owned by Tessera)(under itsSOFTWARE LENS™ trademark). In addition, the following patents, publishedpatent applications, and technical articles are believed to discloserelated EDoF technology: PCT/FR2006/050 197; PCT/FR2008/05 1265;PCT/FR2008/05 1280; U.S. Pat. Nos. 5,748,371; 6,069,738; 7,031,054;7,218,448; 7,436,595; PCT/IL2004/00040; PCT/IL2006/01294;PCT/IL2007/00381; PCT/IL2007/000382; PCT/IL2007/00383;PCT/IL2003/000211; and Dowski & Cathey “Extended Depth of Field ThroughWavefront Coding,” Applied Optics, 34, 11, p. 1859-66 (1995); thecontents of each of which are incorporated herein in their entirety.

Depth of field refers to the depth of the longitudinal region in theobject space that forms an image with satisfactory sharpness at somefocus position. In ordinary optics, the paraxial depth of field isdetermined by the allowable paraxial blur, the lens focal length, andthe lens f-number. See for example, Warren J. Smith, Modern OpticalEngineering, 3rd Edition, Chapter 6. Within the paraxial model, thedepth of field of the lens is fixed once these choices are made.

A more sophisticated model of depth of field in ordinary optics includesthe lens aberrations and diffraction effects. This model typicallyanalyzes the depth of field using through focus Modulation TransferFunction (MTF) calculations. In this model, the depth of focus dependson the aberrations of the lens and the diffraction occurring at thef-number of the lens. The depth of field is determined by these factorsplus the focal length of the lens. As the aberrations become smaller,the depth of field of the lens approaches a limit set by diffraction,which is determined by the lens f-number, the focal length of the lens,and the allowable MTF drop at various object distances. Similarly to theparaxial depth of field model, the maximum depth of field is set by theallowable blur (MTF drop), the lens f-number, and the lens focal length.

In the ordinary optical design process, the goal is to minimize theaberrations present in the lens, consistent with size and costconstraints. The goal is form a sharp image when the lens is in focus.In extended depth of field (EDoF) technology, the depth of field isincreased by a combination of the use of a specially designed lenstogether with EDoF image processing of the image captured by the sensor.Various types of EDoF technology have been proposed or implemented byvarious companies (some of which are mentioned above).

The various EDoF technologies all require that the lens not form thesharpest image possible at best focus, but rather form an image that isdegraded in a special way. In one implementation, this is achieved witha phase mask, which “degrades” the image. In other implementations, thisis achieved by introducing specified monochromatic or chromaticaberrations into the lens design. A sharp image is then recoveredthrough signal processing techniques. The details of how the image isdegraded and how it is recovered differ between the various EDoFtechnologies.

In the design of a lens for use with EDoF technology, the goal is not tominimize the aberrations present in the image formed by the lens, butrather to introduce with the use of a phase mask or a special set ofaberrations into the image formed by the lens that allows recovery of asharp image over an extended depth of field. The exact aberrations ortype of phase mask that must be introduced depends on the particularEDoF technology in use. In some cases, these aberrations are introducedby the addition of an additional optical element, such as a cubic phaseelement (or cubic phase mask), to an otherwise sharp lens. In othercases, axial color or monochromatic aberrations may be introduced intothe lens design itself.

In the example shown in FIG. 1, lens 16 has certain aberrations thereinthat are designed for use with the EDoF processing 20 that will beperformed by the sensor 18 that corresponds to the lens 16. In thisexample, the lens 16 may be a lens having a focal length of 7.2 mm, afield of-view (FOV) of 32 degrees, and an f-number of f/2.8. The lens 12may be a lens having a focal length of 3.62 mm, an FOV of 63 degrees,and an f-number of f/2.8. These lens specifications are merely exemplaryand any other suitable lens characteristics could be acceptable. Inaddition, one or both of the lenses 12 and 16 could be variable focallength (zoom) lenses.

In the example shown in FIG. 1, the two lenses 12 and 16 have the samef-number so that the illuminance of the light received at the sensors 14and 18 is equivalent. With equivalent illuminance, the sensors can beoperated at similar levels of amplification and with similar exposuretimes. In this manner, the separate images captured by the separatesensors 14 and 18 can be of similar levels of brightness and contrast.By having similar levels of amplification, the background noise in eachimage will be similar. By having similar exposure times, artifacts ineach image due to subject motion will be similar. By maintainingsimilarity as to these two characteristics in the two images, thecomposite image formed from the two images will be more acceptable tothe user.

Examples of sensors that could be used for sensor 18 are Model Nos.VD6826 and 69031953 (each of which include DxO EDoF algorithms) andVD68031853 (which includes Dblur EDoF algorithms), each of which areavailable from STMicroelectronics of Geneva, Switzerland. Examples ofsensors that could be used for sensor 14 are these same sensorsmentioned above (with EDoF processing turned off) or similar sensorsthat do not have EDoF capabilities, such as VD6852 or VD6892. In thisexample, each of the sensors is a Bayer sensor, which uses a colorfilter array over the array of separate pixels, as is well known. Suchsensors sense green light at every other pixel, with the interveningpixels alternating between red pixels and blue pixels. The raw sensedsignals are later provided to a demosaicing algorithm, whichinterpolates between the pixels to obtain a full color signal for eachpixel. However, the invention is not limited to use with a Bayer sensorand will work equally well with sensors having a different color filterarray, cameras based on time-sequential color, cameras usingbeamsplitters and separate sensors for each color channel, and othercamera architectures, provided these architectures are consistent withthe operation of one of the underlying EDoF technologies.

In some cases, the camera 10 may be considered to include only thefunctional portions described above. In other cases, these portions(referred to collectively as a camera module 22) may also be combinedwith certain downstream components as part of the camera 10. In suchcase, the camera 10 may also include an image signal processor (ISP) 24,a display 26, and user interface controls 28. Of course, as is wellknown in the camera industry, cameras may also typically include severalother components that are omitted here for simplification. For example,as non-limiting examples, these other components may include batteries,power supplies, an interface for the application of external power, aUSB or other interface to a computer and/or printer, a light source forflash photography, auto-focus and image stability controls, internalmemory, one or more ports for receiving an external memory card ordevice (e.g., an SD or xD memory card), and in the case of the use of acamera in a mobile phone, a microphone, speaker, transmitter/receiver,and an interface for an external microphone and speaker (e.g., aBluetooth headset).

The user interface controls 28 may include conventional controls thatare used to operate the camera, including controls to instruct thecamera to capture one or more images, as well as to manipulate theimages, and many other functions. The display 26 may be a conventionaldisplay that displays images automatically as directed by the ISP 24 orupon request by the user via the user interface controls 28 and ISP 24.The ISP 24 includes certain distortion-correction algorithms thatsmoothly match features between the two separate images when thecomposite image is formed. Further, the ISP 24 may include thedemosaicing algorithm (referenced above with regard to Bayer sensors),sharpening algorithms, and other standard algorithms used in ISPs insuch applications. The ISP also includes algorithms to create thecombined image from the two captured images. A suitable approach forcombining the images is discussed in U.S. Pat. Pub. No. 2008/0030592,referenced above.

FIG. 2 shows both the image 50 from the first sensor (the one with thewider FOV) and the image 52 from the second sensor (the one with thenarrower FOV). The wide FOV image 50 goes through up-sampling 54, whilethe narrow FOV image 52 goes through down-sampling 56. In order toensure that the two images are combined to form a single congruent imagewithout any visible mismatch between the appearance of image objects,the wider FOV image 50 commonly undergoes an image up-sampling operation(i.e. digital zoom) whose scaling factor, A, may range from 1 (i.e. noup-sampling operation applied) to Z, where Z is the ratio of FOV of thefirst sensor to the ratio of FOV of the second sensor. The narrow FOVimage 52 undergoes a down-sampling operation whose scaling factor, B, isgiven by Z divided by A. Hence, the relationship between the two scalingfactors is generally given by the equation:Z=A×B

The amount of up-sampling 54 and down-sampling 56 represents a differenttrade-off between the sharpness quality and the size of the combinedimage. The up-sampling factor is generally controlled by the “digitalzoom” setting selected by the user; however, it is possible to select avalue of A which does not match the “digital zoom” setting in orderconstrain the number of pixels in the combined image. After the wide FOVimage 50 has been up-sampled it may optionally go through furthersharpening 58. Then the wide FOV image 50 has a mask 60 applied thereto,which serves to block a central portion 62 of the image 50 whileallowing a peripheral portion 64 of the image 50 to be used in formingthe combined image 66. After the narrow FOV image 52 has beendown-sampled it has a mask 68 applied thereto, which serves to block aperipheral portion 70 of the image 52 while allowing a central portion72 of the image 52 to be used in forming the combined image 66. Asdifferentiated by a border 74 in the combined image 66, the centralportion 76 of the combined image 66 is taken from the narrow FOV image52 while the peripheral portion 78 of the combined image 66 is takenfrom the wide FOV image 50.

FIG. 3 shows the digital cropping of the peripheral region of thecombined image 66 such that the resulting image has a smaller FOV 80corresponding to the “digital zoom” setting specified by the user. Thismay be referred to as “digital zooming” of the combined image 66. Inthis figure, the central portion 76 of the combined image 66 isdifferentiated from the peripheral portion 78 by the border 74 (althoughthe border 74 will not actually be visible to a user in operation). Inone zoomed image 82, the camera 10 has been zoomed to a position whereonly the central portion 76 of the combined image 66 (which is thenarrow FOV image 52) is used. At the other end of the spectrum, anotherzoomed image 83 can be created, in which the combined image 66 is used.At an intermediate position in the spectrum, a different zoomed image 84can be created. For this image, the central portion 76 of the combinedimage 66 is expanded and only a fraction of the peripheral portion 78 ofthe combined image 66 is used.

Alternatively, the camera module 22 could include one or more ISPslocated thereon. They could be separate from or integrated into thesensors. Further, while the lenses 12 and 16 described herein are fixedfocal length, either or both could be variable focal length (zoom)lenses.

It should be appreciated that with the camera 20 described above, thecombined image will have similar levels of brightness, background noise,motion artifacts, and depth-of field. This will make for a more pleasingand acceptable combined image. If the EDoF technology were not utilized,this would be impossible to achieve. This is because with conventionaloptics it is not possible to get the same illuminance delivered to theimage plane from two lenses of different focal length while at the sametime matching the depth of field. One can choose to have the same imageilluminance; for example, by each of the lenses having an f-number off/2.8. But in such case, the depth of field will be much greater for theshorter focal length lens. Alternatively, one can choose to have thesame depth of field; for example, with the focal lengths for the twolenses used in the example described above in conjunction with FIG. 1,the longer focal length lens would need to have an f-number ofapproximately f/11 to have the same depth of field of the shorter focallength lens. But in such case, the optical power delivered by the longerfocal length lens (at f/11) would be 1/16^(th) of the optical powerdelivered by the shorter focal length. The camera 10 described aboveallows for the optical power and depth of field to be the same for eachlens/sensor combination. Of course, it would also be possible to obtainthe same optical power and depth of field with different focal lengthlenses if the two different image sensors were operated with differentamounts of amplification or with different exposure times.Unfortunately, this would change the background noise level or motionartifact level, respectively, between the two images.

One variation on the disclosure above is that there could be some typeor pre-cropping of the peripheral and central regions of the wide FOVimage prior to the-upsampling operation (to reduce the processing andmemory requirements of the image processing involved in the upsamplingoperation).

Any other combination of all the techniques discussed herein is alsopossible. The foregoing description has been presented for purposes ofillustration and description. Furthermore, the description is notintended to limit the invention to the form disclosed herein. While anumber of exemplary aspects and embodiments have been discussed above,those of skill in the art will recognize certain variations,modifications, permutations, additions, and subcombinations thereof. Itis therefore intended that the following appended claims and claimshereafter introduced are interpreted to include all such variations,modifications, permutations, additions, and sub-combinations as arewithin their true spirit and scope.

We Claim:
 1. A camera, comprising: a first sensor that captures a firstimage; a first lens that directs light to the first sensor, the firstlens having a first focal length and having an f-number; a second sensorthat captures a second image; and a second lens that directs light tothe second sensor, the second lens having a second focal length that islonger than the first focal length and having an f-number substantiallyequal to that of the first lens; and wherein the combination of thefirst sensor and the first lens are substantially aligned with thecombination of the second sensor and the second lens to allow each to bedirected toward the same subject; the first and second images arecombined together to form a single combined image with the second imageforming a central portion of the single combined image and a peripheralportion of the first image forming a peripheral portion of the singlecombined image; the combining of the first and the second imagesincludes up-sampling the first image and down-sampling the second image;and the first image is sharpened after the up-sampling.
 2. A camera asdefined in claim 1, wherein the up-sampling is performed with a scalingfactor A and the down-sampling is performed with a scaling factor B. 3.A camera as defined in claim 2, wherein Z is the ratio of the field ofview (FOV) of the first sensor to the FOV of the second sensor, andZ=A×B.
 4. A camera as defined in claim 3, wherein A is a value in therange between and including 1 and Z.
 5. A camera as defined in claim 2,wherein A is a value in the range between and including 1 and Z, where Zis the ratio of the field of view (FOV) of the first sensor to the FOVof the second sensor.
 6. A camera as defined in claim 1, wherein thefirst image has a mask applied to it before it is combined with thesecond image, the mask blocking a central portion of the first image andallowing a peripheral portion to be used in forming the combined image.7. A camera as defined in claim 1, wherein the second image has a maskapplied to it before it is combined with the first image, the maskblocking a peripheral portion of the second image and allowing a centralportion to be used in forming the combined image.
 8. A camera,comprising: a first sensor that captures a first image; a first lensthat directs light to the first sensor, the first lens having a firstfocal length and having an f-number; a second sensor that captures asecond image; and a second lens that directs light to the second sensor,the second lens having a second focal length that is longer than thefirst focal length and having an f-number substantially equal to that ofthe first lens; and wherein the combination of the first sensor and thefirst lens are substantially aligned with the combination of the secondsensor and the second lens to allow each to be directed toward the samesubject; the first and second images are combined together to form asingle combined image with the second image forming a central portion ofthe single combined image and a peripheral portion of the first imageforming a peripheral portion of the single combined image; the combiningof the first and the second images includes up-sampling the first imageand down-sampling the second image; and at least one of the first imageand the second image has a mask applied to it before the first image andthe second image are combined together, the mask blocking a portion ofthe image to which the mask is applied.
 9. A camera as defined in claim8, wherein the mask is applied to the first image, the mask blocking acentral portion of the first image and allowing a peripheral portion tobe used in forming the combined image.
 10. A camera as defined in claim8, wherein the mask is applied to the second image, the mask blocking aperipheral portion of the second image and allowing a central portion tobe used in forming the combined image.
 11. A camera as defined in claim8, wherein the up-sampling is performed with a scaling factor A and thedown-sampling is performed with a scaling factor B.
 12. A camera asdefined in claim 11, wherein Z is the ratio of the field of view (FOV)of the first sensor to the FOV of the second sensor, and Z=A×B.
 13. Acamera as defined in claim 12, wherein A is a value in the range betweenand including 1 and Z.
 14. A camera as defined in claim 11, wherein A isa value in the range between and including 1 and Z, where Z is the ratioof the field of view (FOV) of the first sensor to the FOV of the secondsensor.
 15. A camera, comprising: a first sensor that captures a firstimage; a first lens that directs light to the first sensor, the firstlens having a first focal length and having an f-number; a second sensorthat captures a second image; and a second lens that directs light tothe second sensor, the second lens having a second focal length that islonger than the first focal length and having an f-number substantiallyequal to that of the first lens; and wherein the combination of thefirst sensor and the first lens are substantially aligned with thecombination of the second sensor and the second lens to allow each to bedirected toward the same subject; the first and second images arecombined together to form a single combined image with the second imageforming a central portion of the single combined image and a peripheralportion of the first image forming a peripheral portion of the singlecombined image; the combining of the first and the second imagesincludes up-sampling the first image with a scaling factor A anddown-sampling the second image with a scaling factor B; Z is the ratioof the field of view (FOV) of the first sensor to the FOV of the secondsensor; and Z=A×B.
 16. A camera as defined in claim 15, wherein A is avalue in the range between and including 1 and Z.
 17. A camera,comprising: a first sensor that captures a first image; a first lensthat directs light to the first sensor, the first lens having a firstfocal length and having an f-number; a second sensor that captures asecond image; and a second lens that directs light to the second sensor,the second lens having a second focal length that is longer than thefirst focal length and having an f-number substantially equal to that ofthe first lens; and wherein the combination of the first sensor and thefirst lens are substantially aligned with the combination of the secondsensor and the second lens to allow each to be directed toward the samesubject; the first and second images are combined together to form asingle combined image with the second image forming a central portion ofthe single combined image and a peripheral portion of the first imageforming a peripheral portion of the single combined image; the combiningof the first and the second images includes up-sampling the first imagewith a scaling factor A and down-sampling the second image with ascaling factor B; A is a value in the range between and including 1 andZ; and Z is the ratio of the field of view (FOV) of the first sensor tothe FOV of the second sensor.